Upstairs radiators won't warm up

[David0123]

Help please, my upstairs radiators won't warm up

The boiler is a cast iron Potterton, more than 20 years old. There are three twin pipe CH circuits, one upstairs, one original downstairs and one "new" downstairs circuit added more than ten years ago. The hot water is a gravity cicuit. Both downstairs circuits and the hot water work fine. The upstairs always used to work fine but has not worked this heating season. This was not a problem until the cold weather and my sons' return from Uni. I have been looking at the problem over Christmas and now have run out of ideas.

Part of the problem is that the symptoms keep changing. The upstairs circuit splits into two. The first radiator on each leg can get warm but not both of them at the same time. The feed pipe to the TRV of one of them can get hot while the radiator may be warm or hot. When this radiator gets hot it doesn't get hot all the way along, that is side to side not top to bottom. The first radiator on the other leg I have not yet got beyond warm. I have not yet got hot water along the feed pipe past the first radiator on either leg.

I took one of the upstairs radiators out to see if it was full of sludge and it was remarkably clean. I have flushed the system through, tried back flushing and refilled it, adding 2 litres of Sentinel X400. This has been circulating for nearly a week now and things aren't any better. All radiators have been bled to death. Turning all the downstairs radiators off doesn't make upstairs noticeably better - I'm very puzzled as to where all the heat goes when I do this.

One other point of possible relevance is that we had the hot water cylinder changed this summer so the system was partially drained. Otherwise the system hasn't changed since it was last working. So what can take out all the upstairs radiators at once? The upstairs circuit doesn't seem to be completely blocked or, surely?, I couldn't get an upstairs radiator to get at all warm.

Any suggestions?

 

[David0123]

One thing I forgot to mention. When I started looking at the problem I found some thin jelly like stuff floating in the F&E tank. It would disolve if I rubbed it between my fingers. Before I started flushing I washed it away down the overflow pipe. The F&E tank has a close fitting cover as well as being in an insulated box so I assume the stuff has come out of the CH system rather than fallen in the tank.

Has anyone seen anything like this, or any ideas where it came from?

 

[JohnD]

1) the jelly is a fungal growth. Clean it out, bale out the F&E to remove all water and mud, and sponge it clean, then wipe it round with a sponge and bleach. Also wipe the lid. This will slow it down a bit while you do your other plumbing work, especially if the loft is very cold. When you think you have finished and are not going to drain and refill again, buy a bottle of Fernox AF-10 Universal Biocide. Empty and clean the F&E again and sponge it round with AF10, then stir half of it into the F&E after refilling. It is quite expensive which is why I say wait until you have finished other work before adding it. You might have to order it from a local plumbers merchant.

Keep an eye on the F&E and use the other half-bottle if you get a recurrence. You may need to treat annually. A full bottle will treat up to 200 litres, but a typical domestic installation is about 100 litres, which is why I say start with half a bottle. It is best added to a clean system (see (3) below.

BTW the depth of water in the F&E only needs to be a couple if inches above the outlet pipe near the bottom. This gives more room for expansion.

2) Turn off all the hot radiators and see if the cold ones then warm up. If so you need to rebalance the rads. You only need about half a turn from closed on the lockshields. Unless you buy pipe thermometers or a laser heat gun, adjust so the flow is "too hot to hold" and the return is "too hot to hold for long"

3) If any of the radiators have cold patches in the middle or at the bottom, or you have black water or other signs of sludge, you can use a sediment-loosening chemical cleaner such as Sentinel X400. Leave it circulating for 4 weeks then drain and rinse. You will know the cleaner is starting to work when the water goes jet black with loosened sediment. As you have an open-vented system that sounds quite old, it probably has a lot of sludge in it. On final fill, add a corrosion-inhibitor such as Sentinel X100 at final fill. These chemicals will cost you about £15 each. Avoid cheap substitutes. Fernox and Sentinel are very good.

 

[David0123]

John, Thank you very much for these helpful suggestions, as soon as I can face the loft temperature I'll try them out.

An additional question please if you can help. Is it possible that the upstairs heating circuit has fungal growth that is stopping the circulation? I've already added 2 litres of X400. Will this dissolve any of the fungal growth that might be in the upstairs radiators and pipework? Or do I need to add some biocide now to try to clear it out?

 

[JohnD]

AFAIK X400 only clears the corrosion sediment. The fungal jelly (I would have thought) would be killed by the high temperature inside the boiler and I have only seen it in an F&E. I would not have thought it could cause a blockage unless it managed to collect inside a pipe with very little flow. I have had it, and it is stringy but I haven't seen it set as firm as the sort of jelly you eat with custard. Try closing the other rads and see if that will cause flow through your cold rads.

I think you have to bale it out of the F&E, I think if you just kill it, it is still stringy. I once put some in a glass jar and added a drop of bleach to see.

If you have a total blockage with absolutely no flow, chemicals don't help as they don't flow into the blockage. However they will often loosen a partial blockage. You could turn off all the rads except one, and see if that gets hot. If not, search for a bypass, and verify that the circulation isn't all going to the HW cylinder (it may have a controlling valve on the pipe to prevent that)

BTW I have previously cleaned an old system with Gravity Cylinder flow, and fitted a Magnaclean. It appeared to be perfectly clean until I converted the HW to fully pumped, whereupon a great deal of old sediment appeared that had obviously been lurking in the pipes and coil.

I am not a pro, but an experienced householder.

p.s. When you added the X400, did you drain out a couple of buckets of water out of the drain cock, to draw it down from the F&E?

 

[David0123]

John - Following your suggestions, thank you again.

I have shut off all the downstairs rads at the TRVs. At the boiler the outgoing HW feed and CH feed are too hot to touch. The return CH pipes are cold. The ingoing pipe to the pump is too hot to touch so I assume that most flow is going round the bypass. The bypass has a gate valve in it which is open just a crack, I have tried not to change it from where it was set. There doesn't appear to be a pressure valve in the bypass.

Upstairs the first radiator in leg 1 of the circuit is slightly warm - but it was the same sort of temperature with the downstair rads on. The feed pipe is hot(ish) but I can grip it firmly with a bare hand without any problem. Lifting a floor board the feed pipe to the next radiator is hot for a couple of feet only. (This is progress when I started no heat got past the first radiator tap off.) The first radiator in leg 2 is cold. So I reckon I must be getting a little flow through at least part of the upstairs circuit.

What is the risk in shutting the bypass completely? It will presumably up the pressure in the CH circuit if it is blocked but will I overheat the boiler?

For the X400 - I drained the system more or less completely, back flushed it until water got back to the F&E tank, drained it again, put the X400 in the tank and let it refill.

I've been trying to think what the jelly reminds me of, it is not stringy, it is a bit like what is left in a bucket of wallpaper paste.

 

[TicklyT]

....we had the hot water cylinder changed this summer....

Just wondering if the new hot cylinder could be taking more than it's fair share of the flow, adding to the problem....

 

[David0123]

Problem solved. I don't know how unusual this has been but it might help someone in future. The X400 wasn't getting anywhere. I tried flushing the feed circuit to the upstairs radiators by taking off the TRV at a radiator and putting a hose on with a compression fitting. I found a compression joint before the boiler I could undo to catch the flushing water before any crud went back into the boiler. Disappointingly this didn't produce any obvious rubbish. When I put it all back together it wasn't improved. However when I tried to bleed the radiator when I was refiling the system I noticed that if I had the lock valve at the radiator outlet shut and only the TRV at the inlet open I couldn't refilll the radiator compltely. (I thought I had done this test more than once but there must have been a backfeed through the return circuit each time.) So I looked more closely at the feed circuit from the boiler and I found under the pipe insulation what looked like an in-line isolating valve which when I removed it turned out to be a non-return valve. The spool was covered with black crud and the rubber seal was swollen. It must have been letting just a small tickle of water upstairs enough to partly warm one radiator.

As I couldn't get a matching spare on a Sunday I have put it back together without the spool and I have hot radiators upstairs. My understanding is that this valve is meant to stop gravity circulation round the radiators when only the hot water is on so I suppose I need to replace the valve some time.